Low-cost hydrocarbon membrane enables commercial-scale flow batteries for long-duration energy storage

Summary

Future terawatt-scale deployment of flow batteries will require substantial capital cost reduction, particularly low-cost electrolytes and hydrocarbon ion exchange membranes. However, integration of hydrocarbon membranes with novel flow battery chemistries in commercial-scale stacks is yet to be demonstrated. Here, we report the pilot-scale synthesis and roll-to-roll manufacturing of sulfonated poly(ether ether ketone) (SPEEK) membranes and demonstrate their high hydroxide conductivity and chemical stability in kW-scale alkaline-based flow batteries. The membrane was integrated in flow battery stacks with power up to 4,000 W, which demonstrated a high energy efficiency of 85.5% operated at 80 mA cm⁻² and long-term stable operation over 800 h as well as substantial cost savings relative to Nafion membranes. This work illustrates a potential pathway for manufacturing and upscaling of next-generation cost-effective flow batteries based on low-cost hydrocarbon membranes developed in the past decades to translate to large-scale applications for grid energy storage.